Apparatus for detecting a condition of a medication infusion system and providing an informational signal in response thereto

ABSTRACT

A medication infusion system having a means for providing an informational signal when (1) medication in the reservoir falls below a threshold level; (2) a fluid leak occurs in different portions of the system; and (3) the intended medication pumping does not correlate with the pumping actually affected.

STATEMENT OF GOVERNMENTAL INTEREST

The invention described herein was made in the performance of work underNASA Contract No. NDPR S-6383B and is subject to the provisions ofSection 305 of the National Aeronautics and Space Act of 1958 (72 Stat.435; 42 U.S.C. 2457).

REFERENCE TO RELATED CASES

This is a divisional of pending U.S. Pat. application filed on Nov. 4,1982, Ser. No. 439,139 now issued into U.S. Pat. No. 4,619,653, which inturn is a continuation in part of Ser. No. 034,155 filed on Apr. 27,1979, and now U.S. Pat. No. 4,373,527. The inventor in the related caseswas Robert E. Fischell.

FIELD OF THE INVENTION

The present invention relates to apparatus for detecting selectedconditions, including deviations in nominal performance, in a system fordispensing medication to a living being. Although mainly intended foruse with human patients requiring infusions of a drug, such as insulin,morphine, heparin, or any of various other chemotherapeutic agents, theinvention extends to use in any living body (such as domestic animals)and to the infusion of any liquid (such as blood) or colloidalsuspension, or gas or granulated solid, which may be dispensed by thesystem and many provide a curative or healing effect. Although aprincipal use of the invention is in implantable devices, the principlesof the invention also apply to systems external to a living being forthe infusion of medication.

TECHNOLOGICAL CONTEXT OF THE INVENTION

Various techniques and devices have been suggested and are currentlyunder study which address the problem of dispensing a drug or othermedicative liquid into a living body. Of these techniques and devices,however, the provision of redundant safety features and the indicationof certain vital operation conditions are rarely addressed and then toonly a limited extent.

One liquid infusion device discussed in U.S. Pat. No. 4.077,405 byHaerton et al discloses a controllable dosing arrangement which providesfor human operator interaction. A syringe forces liquid through apressure valve into a supply reservoir and a bellows pump forces drugfrom the reservoir through a flow limiter into the body. The Haerton etal patent teaches an "overpressure" technique where liquid in thereservoir is at a pressure above that at the discharge point. Thisdevice fails to address various safety problems such as leakage,excessive pumping, and excessive requests for drug. In particular,should the input control valve in this patented device leak, a flood ofliquid would enter the body because of the pressure differential and thelack of any back-up safety mechanism. No provision for detecting leaksin the device, for signalling selected deviation in nominal performance,for restricting the number of or quantity of drug doses, or formonitoring proper operation of the device is suggested.

Like Haerton et al, Ellinwood in U.S. Pat. No. 3,692,027 teaches animplanted, self-powered drug dispenser having a bellows pump which isfed through and expels drug through valves, in particular one-wayvalves. The Ellinwood device is not programmable; it varies dosage byopening and closing portals or selecting a dose of medication from oneof a plurality of pumps having different dosage volumes and/or differentmedications stored therein. System operation relating to pressureintegrity checks during filling, leakage problems, patient and doctorinteraction with the dispenser, and dosage input programming, andinformational outputs which correspond to such system operationconditions are not considered.

An invention of Blackshear (U.S. Pat. No. 3,731,681) shows anotherinfusion pump without such features. While disclosing an implantedbellows pump arrangement fed through a self-sealing plug, the Blackshearpump does not look for pressure integrity before filling the device withdrug. Further, because there is no input check valve and because thepressure in the device is above that of the body in which it isimplanted, leakage in Blackshear can be dangerous. This is particularlytrue because the full reservoir will typically contain a lethal dose ofmedication if delivered over a short period of time. It is thusparticularly significant that no means for indicating to a patienteither proper or non-optimal performance is provided.

Richter (U.S. Pat. No. 3,894,538) considers, in a medicine supplyingdevice, one safety feature: an exit plug for preventing contaminantsfrom entering the device and for limiting drug outflow. However,redundant safety backed up by an informational signal providing featureis absent.

A device by Jacob (U.S. Pat. No. 4,033,479) provides a bellows pumpwhich maintains drug in a chamber at a "constant internal pressure." Avalve opens to release drug from the chamber into a body. The bellowsvaries the chamber volume to maintain constant pressure. It is not ofimportance to Jacob how much pressure there is in the chamber--it isabove body pressure--but, rather, the concern is to keep pressureconstant. Leakage out from the valve and the spurting of drug into thebody under relatively high constant pressure would appear to be problemsinherent in the Jacob device. Apparatus informing a patient of suchconditions or other such conditions is not present.

Portner in U.S. Pat. No. 4,126,132 and its predecessor case, Ser. No.599330 filed July 28, 1976, discuss the use of alarms in an intravenousdelivery system. Sensors for detecting air in the delivery lines bymaking pressure measurements and sensors for detecting the amount offluid in a supply bottle provide input to an audible or visual alarm.The use of alarms for a broad variety of conditions--which alarms wouldincrease the safety of the system--is not discussed. Furthermore, theapplication of alarms to implantable medication release systems is notconsidered.

Franetzki et al U.S. Pat. No. 4,191,181 suggests the use of negativepressure, external to the medication reservoir, as a safety feature in amedication dispensing unit. However, this reference has no teaching ofmeans for detecting and alerting the patient and/or physician regardingthe structural and operational state of the unit, so as to provideinformation regarding e.g. leaks detected within the unit, excessivemedication requests, stored medication level, blockage of the medicationdispenser's output, etc.

Several recent publications have also underscored the advantages of amedication infusion device which is implantable. Two articles by Rhodeet al ("One Year of Heparin Anti-coagulation;" Minnesota Medicine;October, 1977 and "Protracted Parenteral Drug Infusion in AmbulatorySubjects Using an Implantable Infusion Pump"; American Society forArtificial Internal Organs Transactions, Volume XXIII; 1977) describe animplantable infusion pump which comprises a hollow disk separated intotwo chambers by a bellows. A volatile fluorocarbon in the outer chamberforces drug from the inner chamber through a filter and catheter into apatient. Filling of the inner chamber is accomplished by penetrating aself-sealing septum which apparently forms a wall of the inner chamber.The condensation of the fluorocarbon provides energy for cyclicalpumping. No antechamber, no check for pressure integrity before fillingor during operation, no programming means, and no patient or doctorinteraction with the device are contemplated. Detecting the status ofsuch elements and providing corresponding informational signals are thusnot considered.

Finally, an article by Spencer ("For Diabetics: an electronic pancreas;"IEEE-Spectrum; June, 1978) discusses current trends in the drug pumpfield. Preprogramming the rate of drug flow over time depending on foodintake is mentioned. Efforts in the development of a bellows pump arealso discussed. Spencer further mentions the use of alarm sounds if apump fails to provide drug in accordance with the preprogrammed rate.The Spencer article generally discusses drug dispenser technology butfails to address many specific problems. As in other cited systemsredundant safty features such as providing an antechamber; leakdetection; providing distinctive subcutaneous stimulation or audio alarmto indicate various selected conditions and deviations in nominalperformance; providing a safe method of programming the deviceregardless of work, food-intake, or time schedules; and maintaining thereservoir pressure below ambient body pressure so that a leak wouldresult in body fluids entering the device as opposed to a fatal dose ofdrug entering the body (at a high, constant pressure) are notconsidered.

SUMMARY OF THE INVENTION

In a field where safety and reliability are paramount, the presentinvention provides extensive redundancy to prevent and, if appropriate,inform a patient of less than optimal system performance.

According to the medication infusion system described in theabove-identified, related patent application, an antechamber isprovided, which is filled with saline solution or a bacteriacidalsolution or a non-lethal volume of the medication, to act as a bufferbetween the medication intake point and a medication reservoir in thedevice. The medication reservoir may contain a lethal dose of drug orother medication if released all at once. The input to the medicationreservoir is thus isolated from the body by a filter, a one-way inletvalve, the antechamber and a septum which serves as a self-sealingopening to the antechamber. All of these elements are provided toprevent the leakage of medication from the medication reservoir into thebody. As a further measure however, the medication reservoir ismaintained at a pressure below the ambient body pressure. Thus, even ifthe inlet valve and septum leak, body fluids would enter the antechamberand ooze very slowly into the medication reservoir through theflow-impeding filter. A pressure build-up in the medication reservoirwould be detected and an informational signal generated, indicating thatthe relative negative pressure in the medication reservoir hadincreased. On the one hand, the likelihood of a leak out is diminishedand, on the other, the patient is informed if a leak out path exists.Further, any other leak to or from the medication reservoir would besensed by a moisture detector outside the reservoir and an indicativeinformational signal generated.

Also at the outlet where medication from the medication reservoir isdispersed is an element for counting dispensed dosages of medication,which count can be compared to medication requests, thus providing anoperational indicator and safety feature. If, for example, the pulsatilepump fails to function or its output is blocked (e.g. at the catheter),there will be a significant count discrepancy, and an informationalsignal will be provided. This feature would be of great significance inany medication infusion system whether the dispensing pump is implantedor external to the body.

In programming the medication infusion system, convenience and safetyare major concerns. Thus, in addition to a programmable rate ofmedication input, a hardwired limit is also included to limit thedispensing of medication. If requests exceed the limits set by theprogram, the hardwired limits will inhibit the pulsing of excessivemedication into the patient and an informational signal to the patientwill be provided.

Safe filling is also a concern in the present invention. To assure thatthe patient receives the proper medication, a matching procedure ofpatient to medication is employed. If an identification code on themedication does not match a patient identification code, it will not beinjected into the medication reservoir from which dispensing takesplace. Like the bar coding of consumer products, a similar medicationcoding correlated to a patient and his needs is provided. An attempt atrefilling a patient's unit with improper medication will prompt awarning signal to the physician. Filling the reservoir is also performedin a safe manner, with an indicator signal being activated when thereservoir is filled.

The informational signal to be provided when an improper operationalcondition is sensed can take various forms. A subcutaneous electrical,thermal, or acoustic signal in the form of a single pulse or multiplepulses which can have various pulse widths or pulse intervals can informthe patient of an existing or potentially undesired operating conditionor proper operation if that is desired. In addition, provision is madefor a physician to interrogate the medication infusion system todetermine exactly what the condition is that is causing the alarm. Forsome patients the physician may wish to have the same informationalsignal provided for each different alarm with a unique signal (dependingon the cause of the alarm) being made known by telemetry but onlydiscernible by the physician.

The physician could also be provided with a means to disable any of theinformational signals for a variety of reasons. For example, if themoisture detector became defective so that it incorrectly caused aninformational (alarm) signal to be generated, then the physician mayelect to turn that alarm off rather than surgically removing the deviceimplanted in the patient. A telemetry means can be provided to determinewhich informational signals are enabled and which, if any, are disabled.

Various informational signals to indicate low battery voltage,medication reservoir nearly empty of medication, and medication infusionpump switched off are provided which could enhance the safe operation ofan implanted or external pump in a medication infusion system.Additionally, indications are given when refill of the medicationreservoir has been completed and if moisture is detected either betweenthe reservoir and the outer casing or inside the compartment housing theelectronics portion of the medication infusion system.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a general block diagram of amedication infusion system employing the present invention.

FIGS. 2 and 3 are illustrations showing a front cutaway and a topperspective view, respectively, of a medication dispensing unit in amedication infusion system.

FIG. 4 shows, in detail, a top view of a combination moisturedetector/switching unit which senses when various predeterminedoperating conditions exist.

FIG. 5 is a cross-section side view of the combination moisturedetector/switch unit shown in FIG. 4.

FIG. 6 shows one embodiment of an informational signal generator.

FIG. 7 is a cross-section view of one embodiment of a pump which may beincluded in the present system.

FIG. 8 is a block diagram showing electronic components of the system.

FIG. 9 shows signals representing various pulse-coded alarm patternsused in informing a patient of various deviations from normal operatingconditions.

DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the various portions of a programmable medicationinfusion system are shown. A medication dispensing unit 10 inplantablein or external to a patient's body can be programmed either by themedication programming system 12 or by the patient is programming unit14. Commands from the medication programming system 12 emitted from thecommunication head 16 are transmitted to electronics in the medicationdispensing unit 10 in order to program and effectuate the infusion ofmedication into the body in a safe, controlled fashion. Furthermore, thecommunication head, 16, is used to receive signals telemetered out ofthe implanted unit 10. Thus, the communication head, 16 is really acommand transmitting antenna and a telemetry receiving antenna. Thisantenna might typically be a few hundred turns of fine copper wirehaving approximately the same diameter as a similarly configured antennain the implanted medication dispensing unit 10. The communication head16, might also provide a source of an alternating magnetic field coupledto the similar coil in the implanted unit 10, to provide energy forrecharging a rechargeable cell contained in 10. Furthermore theinductively coupled energy could be used to power the command andtelemetry systems of the implanted unit 10.

The medication programming system 12 is also capable of readinginformation telemetered out from the medication dispensing unit 10,which information relates to the amount of medication dispensed over aspecified time period as well as other data of value to the physician.Further, the medication programming system 12 is capable of calibratingthe medication per pulse which is dispersed by the medication dispensingunit 10. A medication injection unit 18 is connected to a doublehypodermic syringe 20 which is used to provide medication to amedication reservoir 22 (shown in FIG. 2) included within the medicationdispensing unit 10. Fill commands to the medication injection unit 18emanate from a medication programming unit 24. A patient's programmingunit 14 (which may also communicate, by inductive transmission forexample, with the medication dispensing unit 10) is controlled by theuser (typically the patient) to request doses of medication, i.e. toobtain self-medication. The dispensing of dosage requests is limited byvarious elements included in the programmable memory units (shown inFIG. 8 as 106 and 108) and in the hardwired limit controls (shown at 110and 112 in FIG. 8) all of which are found in the medication dispensingunit 10.

To recharge a power cell 26 (see FIG. 8) contained within the medicationdispensing unit 10 (when the power cell 26 is a rechargable type), anexternal charging head 28 connected to a battery charging unit 30 isincluded. The need for the charging head 28 and battery charging unit 30can be obviated by the inclusion in the medication dispensing unit 10 ofa power cell 26 (such as a lithium cell) which is of sufficient lifetimeto negate the need for recharging. Where the implantable portion 10 is,in fact, not implanted but is employed externally other methods ofrecharging or even replacement of the power cell may be employed. Themedication programming unit 24 provides output to a paper printer 32which provides hard, readable output that can be readily interpreted bya physician.

Referring now to FIGS. 2 and 3, the medication dispensing unit 10 of animplantable programmable medication infusion system is shown. Medicationis provided to the medication dispensing unit 10 by means of ahypodermic syringe 20 which penetrates the skin 34 and passes through aconical aperture 35 and a self-sealing septum 36, preferably made ofmedical grade silicone rubber or the like, which covers an antichamber38 in leak-proof fashion. Medication is introduced into the antechamber38 through syringe 20 at atmospheric pressure or under pressure thelevel of which is controllable externally. A medication reservoir 22, inwhich the medication is stored under relatively constant pressure, isfed from the antechamber 38 via a ceramic filter 43 and a one-way inletpressure valve 44 which permits flow only from the antechamber 38 intothe medication reservoir 22 when the pressure differential between themexceeds a predetermined threshold.

The inlet cermic filter 42 surrounds the antechamber 38 and performsvarious functions which enhance the safety of the implantable portion 10particularly in an implant environment. Besides filtering contaminantsfrom medication being fed into the medication reservoir 22, the ceramicfilter 42 serves to limit the rate of medication flow from theantechamber 38 into the reservoir 22 or, conversely, from the reservoir22 into antechamber 38 should the inlet pressure valve 44 leak. Shouldthe septum 36 leak, the ceramic filter 42 together with the inletpressure valve 44 prevents the inflow of body fluids into the medicationreservoir 22. Further, should the inlet pressure valve 44 and the septum36 both leak or otherwise deviate from optimal performance, the filter42 would permit only a slow flow of body fluids to enter the medicationreservoir 22, until body ambient pressure is achieved, at which timesome medication could diffuse through the ceramic filter 42 but at arate that would not be hazardous to a typical patient in which thesystem would be implanted. Furthermore, when this occurs aninformational signal would be generated.

A liquid-vapor pressurant chamber 45 is separated from medicationreservoir 22 by a flexible diaphragm 46a. The liquid-vapor volume in theliquid-vapor chamber 45 preferably comprises a saturated vapor inequilibrium with a small amount of Freon 113 liquid. Over normal bodytemperatures, Freon 113 has a linear pressure characteristic rangingfrom -4 psig (at 98°) to approximately -2.5 psig (at 104° F.). UsingFreon 113, the medication reservoir 22 will be maintained at a pressurebelow that of the human body pressure up to altitudes of 8500 feet. Forpatients who may live above the altitude, other fluorocarbons at lowerpressure may be employed. In this way, should both the septum 36 and theinlet pressure valve 44 leak, the effect would be to cause body fluidsto diffuse slowly through the inlet ceramic filter 42, into themedication reservoir 22 rather than to have a rapid flow of medicationenter into the body where it could cause harm to the patient. Because ofthe pressure differential between the body and the medication reservoir22, medication will not flow from the reservoir 22 into the body. As theamount of medication in the medication reservoir 22 varies, the flexiblediaphragm 46a moves up or down, with the Freon 113 being convertedeither from liquid to vapor or vapor to liquid to provide an essentiallyconstant pressure which will always be below one standard atmosphere andbelow normal body pressure. A medication reservoir 22 having a volume ofapproximately 10 cc would be sufficient for most applications. Thisamount of concentrated medication, insulin for example, could be fatalif injected over a short time. To prevent fatal leakage, the volume ofthe antechamber 38 is designed to have a safe dosage volume, e.g. lessthan 10% the size of the medication reservoir 22. In the worst case, ifthe medication reservoir 22 had a leak into the antechamber 38 whichalso had a leak, only medication diluted with incoming body fluids dueto the pressure differential would initially enter the body. Such flowwould be at a relatively slow diffusion rate because there would be zeropressure differential and because there is very restrictive flow path.Under these conditions, the likelihood of leakage being fatal isminimized. As readily seen in FIG. 2, varying the size or shape of themedication reservoir 22 would be a simple modification because of thearrangement of elements in the system. A very important characteristicof the reservoir is that it is all metal (including the diaphragm 46a ofFIG. 2.) so that no moisture can diffuse out of the reservoir 22 so thatcould damage any of the electronics in the implanted unit 10.

Included in the liquid-vapor chamber 45 of a combined diaphragm positionswitch-moisture detector unit 46 (shown enlarged in FIGS. 4 and 5)comprising a ceramic insulator substrate 47 to which is attached amovable electrical contact 48, and deposited metal surfaces 50, 51, 52and 53. When the medication reservoir is being filled, the flexiblediaphragm 46a will move outward, and when the medication reservoir 22 isfull, the flexible diaphragm 46a will make physical contact with themovable electrical contact 48. Since the flexible diaphragm 46a ispreferably fabricated of metal and is therefore an electrical conductor,it will close an electrical circuit through the movable electricalcontact 48 and the deposited metal surface 50 which can be used to sendout a signal by the telemetering transmitter 105 of FIG. 8, to themedication programming system 12 of FIG. 7, to stop the infusion ofmedication.

If body fluids leak into the medication reservoir 22, the flexiblediaphragm 46a will move out further, resulting in the movable electricalcontact 48 being forced to make electrical contact with the metalsurface 51 of FIG. 4. This switch closure would cause the programmableinformation signal generator 70 of FIG. 8 to provide an appropriateinformational signal which would be sent to warn the patient. By way ofexample, the signal to the patient might be in the form of an electrical"tickle" stimulation applied subcutaneously by means of a stimulationelectrode 51a of FIG. 8 disposed on the upper surface of the unit 10(see FIG. 2). Another useful means for warning the patient would be bymeans of an acoustical transducer typically within the implanted devicethat would provide the patient with an audible alarm.

In the presence of Freon 113, but in the absence of moisture, theelectrical resistance between the deposited metal surfaces 52 and 53which collectively form the moisture detector 54 (see FIG. 8) is greaterthan 1 megohm. If however, moisture is released into the liquid-vaporchamber 45, either through a leaky flexible diaphragm 46a of if bodyfluids leak through the sealed outer cover 60 into the liquid-vaporchamber 45, then the moisture detector 54 will experience a detectabledecrease in electrical resistance across the metal surfaces 52 and 53.If this occurs, moisture detectors 54 initiates an informational signalto be sent to the patient to indicate a leak in the implanted unit 10.

The medication reservoir 22 and liquid-vapor chamber 45 are separatedfrom the other portions of the medication dispensing unit 10 by wall 55(forming the top of reservoir 22, as viewed in FIG. 2) and fluidicallyisolated from the other elements of the system by means of the inletpressure valve 44 and a pump inlet valve 73 (see FIG. 7) which connectsthe reservoir 22 to a pulsatile pump 57 (shown in detail in FIG. 7). Theremaining elements of the implantable medication dispensing unit 10 areshown in FIG. 2 above and isolated from the reservoir 22 (by wall 55)and include an electronics compartment or section 56 containing a powercell subsection 58. As is readily seen in FIG. 2, an outer cover 60isolates the medication reservoir chamber 22 and liquid-vapor pressurantchamber 45 as well as the pump 57 and the electronics compartment orsection 56 (and the power cell subsection 58) from the externalenvironment. A moisture detector 59, of the same design as detector 54described above, would be located in an electronics section 56 (of FIG.2) so that it could detect and provide an informational signal to thepatient if either a medication leak occurs through the wall 55 or bodyfluids penetrate the top portion of the sealed outer cover 60.

An informational signal generator 70, such as that shown in FIG. 6, canbe used in signalling or alerting a patient of a predetermined conditionor in checking the medication dispensing unit 10 (of FIG. 2). Thegenerator 70 has a plurality of inputs A₁ through A_(N). The A₁ throughA_(N) inputs are provided by a command decoder (104 of FIG. 8), theinputs A₁ through A_(N) selectively switching elements S₁ through S_(N)in amplitude select element 72 to provide 2^(N) possible, programmablevoltage levels. The programmable voltage level is applied to anamplifier transistor circuit 74, which is biased by a voltage V_(A). Theoutput signal V_(o) of the circuit 74 can be applied to a lead 75 incontact with the patient if an input (V_(IN)) to a FET 76 is provided. Acapacitor 77, preferably of one microfarad, is located between the alarmoutput signal V_(o) and the patient to generate a patient-sensed voltageacross load R_(p) ranging between one and ten volts selectable inprogrammable steps. The load R_(p) can provide electrical stimulation(e.g. by means of the stimulation electrode 51a in FIG. 2), heat, oraudio alarm output to inform the patient. In the case of aninformational (alarm) signal provided by electrical stimulation, theload Rp is the electrical load caused by the patient's tissue and fluidsurrounding the alarm electrode 51a. When the FET 76 conducts, the loadR_(p) is short-circuited. When the FET 76 is not conducting (there is noV_(IN)), a stimulating signal through the load R_(p) can be effected.The information signal generator 70 input V_(IN) may be high (or "on")when any one of a plurality of selected conditions is detected andsignalled, such as: the fill limit of reservoir 22 has been reached(when diaphragm 46a connects to switch contact 48 in FIG. 5), bodyfluids have entered reservoir 22 (when contact 48 connects to surface51), unwanted moisture has been detected within the unit 10 (by detector54 or 59 in FIG. 8), and the like.

The pump 57 shown in FIG. 7 is discussed in detail in theabove-referenced patent application. In an output chamber of the pump 57is a tranducer 78 which senses when a pulsatile dose of medication isdispensed. Transducer 78 detects pressure build-up in the output chamberof pump 57. It may be noted that other types of transducers areavailable which can detect a pulsatile flow through an output tube. Eachpulse of medication is communicated by the transducer 78 as anelectrical pulse and therefore, based upon prior knowledge of the volumeof medication in reservoir 22 when full and the volume of medicationdispensed for each actuation of pump 57, it is obvious that at any giventime the current volume of medication remaining in the reservoir 22 canbe determined by merely recording a count of the number of pulsesproduced by transducer 78. To promote a pulse of medication, a coil 79(or other similar means of reciprocating a variable volume pump storagechamber 80) is provided with a pulse of electrical energy.

By comparing the number of electrical pulses to the coil 79 with thenumber of electrical pulses produced by the transducer 78, anoperational check is performed and indicates, for example, that theoutput of the medication dispensing system is clogged. Thus, as seen inFIG. 8, electrical pulses from the transducer 78 and a count ofelectrical pulses to the coil 79 are communicated to and stored in apulse recorder 82.

The output of the transducer 78 is also applied to a pulse rate detector84. The pulse rate detector 84 provides a hard-wired "insufficient rate"command input which provides a programmable lower medication dispensinglimit. That is, when less than a physician prescribed minimum ofmedication is delivered to the body, the rate detector 84 signalsinformation signal generator 70 that an informational (alert) signal tothe patient is to be generated. To effect this signal, an input (line84a) to the programmable information signal generator 70 (of FIGS. 6 and8) is connected through switch inputs, such as V_(IN) in FIG. 6.Although shown as a FET switch input, V_(IN) may provide input toanother form of switch connected to a programmable information signalgenerator 70 which may have a pulse coded memory and varied outputscorresponding to inputs for different conditions (as shown in FIG. 8.)Overpressure (from an over-filled reservoir), fluid detection, pulsecount discrepancy, excessive pulse request, low battery voltage, and thelike can thus stimulate an alarm signal by entering a line like V_(IN)of FIG. 6.

For example, the pulse rate detector 84 sends transducer pulse rateinformation to the pulse recorder 82, which information is compared bycomparator circuitry in the pulse recorder 82 to the electrical pulsesover the same period from the coil 79. A discrepancy between the twocounts results in a signal to the information signal generator 70 overline 82a, as seen in FIG. 8 which causes the FET 76 (FIG. 6) to assume ahigh impedance state and a current to pass through stimulation electrode51a. As noted earlier, thermal, acoustic, or other similar stimulationto the body might be used in place of or in combination with theelectrical stimulation.

As seen in FIG. 8, the electronics portion of medication dispensing unit10 (enclosed by dashed line 56 of FIG. 8) communicates with acommunication head 16 which is external to the body (for both implantedand external embodiments). Communication may be by wire for externalembodiments or, for implantable or external embodiments, by radiantenergy (in electromagnetic, alternating magnetic, or other remote signalforms).

The communication head 16, in the FIG. 8 embodiment, provides both powerand command inputs, as well as receiving telemetry output. Morespecifically, input power is provided by means of an alternating field,e.g. a magnetic field, which is communicated to a pickup coil 92 whichis connected to other elements of the electronics section 56. The pickupcoil 91 receives a power signal and passes it on to a full waverectifier 94. One rectified output from the full-wave rectifier 94enters a battery charge control 96 which provides a fixed DC chargingsignal to a power cell 26. The power cell 26 can be a nickel-cadmiumcell which is readily rechargeable off a rectified signal at a typicalfrequency of 20 kHz. Alternatively, a lithium-type solid state batterycan be used instead of the nickel-cadmium cell in which case thecharging circuitry could be eliminated, the lithium-type batteryproviding sufficient power over a long term, thereby obviating the needfor recharging. The power cell 26 provides a biasing voltage to a switch98, the output of which enters the pulsing coil 79 previously described.

In addition to providing power to the power cell 26, rectified power isalso introduced to a DC-to-DC converter 100 the purpose of which is toprovide power at the proper levels to the various loads in the system.In addition to the AC power signal, pickup coil 92 may also receive atrain of serial digital bits, e.g. from the communication head 16. Thedigital bits comprise commands for programmable inputs which areconveyed, via the pickup coil 92 to a command receiver 102. The signalsfrom the command receiver 102 enter a command decoder 104 whichdetermines if the digital bits are in a proper format and, if so, whataction in the system the commands dictate. To allow remote verificationof the information decoded in command decoder 104, the decoded signalsare transmitted back to the communication head 16 by means of atelemetry transmitter 105 and a telemetry coil 107. It should also benoted that the full wave rectifier 94, the battery charge control 96,the command receiver 102, the command decoder 104 and telemetrytransmitter 105 could be powered only when an AC signal is picked up bythe pickup coil 92. As seen in FIG. 8, for example, the command receiver102 receives operating power from the full-wave rectifier 94 enabling itto convey signals from the coil 92 to the command decoder 104. It shouldbe obvious that a power savings is achieved by only powering the commandreceiver etc. when necessary and, moreover, prevents the possibility ofdetecting stray signals as commands. To be sure, the power savingsachieved could make possible the use of the aforementioned lithium cellwhich would not require recharging.

From the command decoder 104, programmable inputs and other commands canbe provided to a number of elements. A programmable base rate is enteredinto a base rate memory unit 106 which stores a value indicating thenumber of pulses of medication which are to be provided to a patientduring a normal preselected period of time. A second programmable inputis provided to a patient-controlled rate memory unit 108 which stores avalue indicating a number of pulses of medication that are requested bythe patient (with a patient programming unit 14) to be introduced intothe body.

Associated with the base rate memory unit 106 is a hardwired base ratelimit control 110 which sets a maximum rate that can override requestsof the base rate memory unit 108 which are excessive. Similarly, ahardwired patient-controlled rate limit control 112 provides a fixedmaximum number of pulses which can be provided at a time after a meal orat other times and under other conditions such as exercise. As long asthe base rate and patient-controlled rate values stored in memory units106 and 108 respectively, do not exceed the hardwired values fixedwithin limit controls 110 and 112, respectively, an output pulse isprovided to the switch 98 to stimulate a pulse output from pulsing coil79. Should the rate of either memory unit 106 or 108 exceed thehardwired limits in the limit control elements 110 or 112, respectively,a "rate request exceeds limit" signal is fed from the limit controlelement 110 or 112 into the programmable information signal generator 70which provides an electrical signal to the load R_(p). The patient (inone form of the invention) is informed by means of a stimulation thatmore medication than permitted has been requested.

It should be noted that the signal to the load R_(p), e.g. an electrode,can serve the dual function of not only providing the patient with asubcutaneous, heat, or audible stimulation but may also be detected bythe communication head 16, via signal transfer means V_(o), and may becommunicated to the physician, thereby indicating that a deviation fromoptimal system status has occurred. As shown in FIG. 8, the load R_(p)will be isolated and electrically insulated from the outside of theenclosure 60 of the medication dispensing unit 10.

A particularly significant feature of the invention resides in theprogrammability of the information signal generator 70 based on inputcommands from the command decoder 104. The voltage produced by thesignal generator 70 across the load R_(p) can be varied in response tosignals emanating from the communication head 16 and channelled throughthe command receiver 102 to the command decoder 104 and into inputs A₁through A_(n) of amplitude select element 72 (shown in FIG. 6).

In addition, in order to check the proper operation of the system, thecommand decoder 104 can receive test signals which can stimulate actualoccurrences to determine whether the circuitry in the electronic section56 is operating properly. For example, extra pulses from the commanddecoder 104 can be entered into the hardwired limit control elements 110and 112. These extra pulses can be added to the pulses provided by thebase rate and the patient-controlled rate memory units 106 and 108, inorder to exceed the hardwired base rate and the hardwiredpatient-controlled rate, respectively. When the rates are exceeded, theinformation signal generator 70 will provide a signal. In this way, theinformation signal generator 70 can be used to check the operation ofthe limit control elements 110 and 112, inform the physician ofoperational problems via means V_(o), and also familiarize the patientwith the corresponding stimulation emitted by the load R_(p).

The programmable information signal generator 70 also receives inputsfrom the movable electrical contact 48 and the moisture detectors 54 and59 (see FIGS. 2 and 4). If body fluids leak into the medicationreservoir 22, the movable electrical contact 48 will make electricalcontact with 51, indicating this fault condition to the patient byactivating the information signal generator 70. If the patient wasunconscious, voltage levels on the patient's skin at the site of themedication dispensing unit 10 could be used by the physician to detectif a deviation has occurred and could, with a pulse-coded embodiment,indicate which selected deviation in nominal performance it was.Further, as previously described, should fluid leak out of themedication reservoir 22 or if body fluid should leak in through theenclosure 60, the moisture detector 54 would sense such leakage and, asshown in FIG. 8, would provide input to the information signal generator70. Similarly, moisture detector 59 would signal the presence ofmedication or body fluid in the electronics compartment 56. Stillanother input to the information signal generator 70 comes from thepower cell 26 associated with the transistor switch 98. The voltagelevel of the power cell 26 is thus communicated to the signal generator70; a stimulation signal being generated when the battery voltage isbelow a predetermined level.

It should be noted that the various mentioned conditions in the systemresult in stimulations each of which may all be the same or which may bedifferent in stimulation pulse amplitude, duration, periodicity,interpulse spacing or other coding. For example, the stimulation mayrange between one to ten volts; may vary in frequency over a wide range;and, most importantly, a variety of unique pulse patterns may be used toindicate the various selected conditions or deviations in nominalperformance.

As discussed previously, additional signals to initiate an informationalsignal to the patient are derived from pulse count information in thepulse recorder 82 and pulse rate detector 84 of FIG. 8 and might also bederived from any of a variety of optical, capacitive, inductive, liquidcrystal, or other reservoir level measuring elements which might beutilized to inform the patient (or physician) when say only 10% or a 5days supply of the medication remains in the reservoir.

Referring to FIG. 9, three pulse-coded deviation signals areillustrated. In FIG. 9(A), two 1.5 second signals five seconds apart arerepeated at fifteen minute intervals to indicate insufficient medicationrate. In FIG. 9(B), two 1.5 second signals ten seconds apart arerepeated at thirty minute intervals to indicate a moisture leak. In FIG.9(C), two 1.5 second signals fifteen seconds apart are repeated everyforty-five minutes to indicate that the medication reservoir containsbody fluids. Similar coding or a variation thereof can also be employedto indicate low battery voltage and undesirably high medication raterequests.

It may also be desirable to have the same pattern for all alarms, buthave a unique informational signal be provided only for the physician todetermine the specific cause of that alarm. If that was done, then anyone of the signal formats of FIG. 9 could be used as the alarm patternfor the patient.

Various other modifications, adaptations and alterations are of coursepossible in light of the above teachings. Therefore, it should beunderstood at this time that within the scope of the appended claims theinvention may be practiced otherwise than as specifically described.

What is claimed is:
 1. An apparatus for infusing medication into aliving body comprising:a medication reservoir means for storingmedication to be infused; a pulsatile pump means operably coupled tosaid reservoir means for pumping a dose of medication in response to anelectrical pulse input; means for applying said electrical pulse inputto said pumping means; an infusion output from which pumped medicationexits the system and is dispensed to the patient; a sensing means,disposed at the infusion output, for sensing the actuation of saidpumping means and the dispensing of a dose of medication and transducingan electrical signal corresponding to each dispensed dose; and, a volumedetecting means for detecting the volume of medication dispensed fromsaid reservoir means, and including,a counting means, operably coupledto said sensing means for counting the occurrences of said electricalsignal corresponding to said dispensing dose, and a means for providingan information signal when said counting means reaches a certain countnumber.
 2. The apparatus of claim 1, wherein said volume detecting meansfurther comprises a means for storing a valve for said count number. 3.The apparatus of claim 1, further comprising:an acoustic transducer;and, a means responsive to said informational signal for actuating saidacoustic transducer.
 4. The apparatus of claim 1, further comprising:atickle means adapted for implantation for applying a subcutaneouselectrical tickle to an intracorporeal location; and, a means responsiveto said informational signal for actuating said tickle means.
 5. Asystem for infusing medication into a patient comprising:a pulsatilepump means for pumping a dose of medication in response to an electricalpulse input; means for applying said electrical pulse input to saidpumping means; an infusion output from which pumped medication exits thesystem and is dispensed to the patient; means, disposed at the infusionoutput, for sensing the actuation of said pumping means and thedispensing of a dose of medication and transducing a singlecorresponding electrical pulse for each dispensed dose, means, receivinginputs from the electrical pulse transducing means and from theelectrical pulse applying means, for comparing the number of appliedelectrical pulses with the number of transduced electrical pulses; and,means, connected to the comparing means, for generating an informationalsignal when the number of transducer electrical pulses deviate from thenumber of applied electrical pulses.